NSD1 mediates antagonism between SWI/SNF and polycomb complexes and is required for transcriptional activation upon EZH2 inhibition.

Disruption of antagonism between SWI/SNF chromatin remodelers and polycomb repressor complexes drives the formation of numerous cancer types. Recently, an inhibitor of the polycomb protein EZH2 was approved for the treatment of a sarcoma mutant in the SWI/SNF subunit SMARCB1, but resistance occurs. Here, we performed CRISPR screens in SMARCB1-mutant rhabdoid tumor cells to identify genetic contributors to SWI/SNF-polycomb antagonism and potential resistance mechanisms. We found that loss of the H3K36 methyltransferase NSD1 caused resistance to EZH2 inhibition. We show that NSD1 antagonizes polycomb via cooperation with SWI/SNF and identify co-occurrence of NSD1 inactivation in SWI/SNF-defective cancers, indicating in vivo relevance. We demonstrate that H3K36me2 itself has an essential role in the activation of polycomb target genes as inhibition of the H3K36me2 demethylase KDM2A restores the efficacy of EZH2 inhibition in SWI/SNF-deficient cells lacking NSD1. Together our data expand the mechanistic understanding of SWI/SNF and polycomb interplay and identify NSD1 as the key for coordinating this transcriptional control.

Constitutional balanced translocations involving SMARCB1: A rare cause of rhabdoid tumor predisposition syndrome.

Rhabdoid Tumor Predisposition Syndrome 1 (RTPS1) confers an increased risk of developing rhabdoid tumors and is caused by germline mutations in SMARCB1. RTPS1 should be evaluated in all individuals with rhabdoid tumor and is more likely in those with a young age at presentation (occasionally congenital presentation), multiple primary tumors, or a family history of rhabdoid tumor or RTPS1. Proband genetic testing is the standard method for diagnosing RTPS1. Most known RTPS1-related SMARCB1 gene mutations are copy number variants (CNVs) or single nucleotide variants/indels, but structural variant analysis (SVA) is not usually included in the molecular evaluation. Here, we report two children with RTPS1 presenting with atypical teratoid/rhabdoid tumor (ATRT) who had constitutional testing showing balanced chromosome translocations involving SMARCB1. Patient 1 is a 23-year-old female diagnosed with pineal region ATRT at 7 months who was found to have a de novo, constitutional t(16;22)(p13.3;q11.2). Patient 2 is a 24-month-old male diagnosed with a posterior fossa ATRT at 14 months, with subsequent testing showing a constitutional t(5;22)(q14.1;q11.23). These structural rearrangements have not been previously reported in RTPS1. While rare, these cases suggest that structural variants should be considered in the evaluation of children with rhabdoid tumors to provide more accurate genetic counseling on the risks of developing tumors, the need for surveillance, and the risks of passing the disorder on to future children. Further research is needed to understand the prevalence, clinical features, and tumor risks associated with RTPS1-related constitutional balanced translocations.

Molecular classification and outcome of children with rare CNS embryonal tumors: results from St. Jude Children's Research Hospital including the multi-center SJYC07 and SJMB03 clinical trials.

Methylation profiling has radically transformed our understanding of tumors previously called central nervous system primitive neuro-ectodermal tumors (CNS-PNET). While this marks a momentous step toward defining key differences, reclassification has thrown treatment into disarray. To shed light on response to therapy and guide clinical decision-making, we report outcomes and molecular features of children with CNS-PNETs from two multi-center risk-adapted studies (SJMB03 for patients ≥ 3 years; SJYC07 for patients < 3 years) complemented by a non-protocol institutional cohort. Seventy patients who had a histological diagnosis of CNS-PNET or CNS embryonal tumor from one of the new categories that has supplanted CNS-PNET were included. This cohort was molecularly characterized by DNA methylation profiling (n = 70), whole-exome sequencing (n = 53), RNA sequencing (n = 20), and germline sequencing (n = 28). Clinical characteristics were detailed, and treatment was divided into craniospinal irradiation (CSI)-containing (SJMB03 and SJMB03-like) and CSI-sparing therapy (SJYC07 and SJYC07-like). When the cohort was analyzed in its entirety, no differences were observed in the 5-year survival rates even when CSI-containing therapy was compared to CSI-sparing therapy. However, when analyzed by DNA methylation molecular grouping, significant survival differences were observed, and treatment particulars provided suggestions of therapeutic response. Patients with CNS neuroblastoma with FOXR2 activation (CNS-NB-FOXR2) had a 5-year event-free survival (EFS)/overall survival (OS) of 66.7% ± 19.2%/83.3% ± 15.2%, and CIC rearranged sarcoma (CNS-SARC-CIC) had a 5-year EFS/OS both of 57.1% ± 18.7% with most receiving regimens that contained radiation (focal or CSI) and multidrug chemotherapy. Patients with high-grade neuroepithelial tumor with BCOR alteration (HGNET-BCOR) had abysmal responses to upfront chemotherapy-only regimens (5-year EFS = 0%), but survival extended with salvage radiation after progression [5-year OS = 53.6% ± 20.1%]. Patients with embryonal tumor with multilayered rosettes (ETMR) or high-grade glioma/glioblastoma multiforme (HGG/GBM) did not respond favorably to any modality (5-year EFS/OS = 10.7 ± 5.8%/17.9 ± 7.2%, and 10% ± 9.0%/10% ± 9.0%, respectively). As an accompaniment, we have assembled this data onto an interactive website to allow users to probe and query the cases. By reporting on a carefully matched clinical and molecular cohort, we provide the needed insight for future clinical management.

Atypical teratoid/rhabdoid tumors (ATRTs) with SMARCA4 mutation are molecularly distinct from SMARCB1-deficient cases.

Atypical teratoid/rhabdoid tumors (ATRTs) are very aggressive childhood malignancies of the central nervous system. The underlying genetic cause are inactivating bi-allelic mutations in SMARCB1 or (rarely) in SMARCA4. ATRT-SMARCA4 have been associated with a higher frequency of germline mutations, younger age, and an inferior prognosis in comparison to SMARCB1 mutated cases. Based on their DNA methylation profiles and transcriptomics, SMARCB1 mutated ATRTs have been divided into three distinct molecular subgroups: ATRT-TYR, ATRT-SHH, and ATRT-MYC. These subgroups differ in terms of age at diagnosis, tumor location, type of SMARCB1 alterations, and overall survival. ATRT-SMARCA4 are, however, less well understood, and it remains unknown, whether they belong to one of the described ATRT subgroups. Here, we examined 14 ATRT-SMARCA4 by global DNA methylation analyses. We show that they form a separate group segregating from SMARCB1 mutated ATRTs and from other SMARCA4-deficient tumors like small cell carcinoma of the ovary, hypercalcemic type (SCCOHT) or SMARCA4 mutated extra-cranial malignant rhabdoid tumors. In contrast, medulloblastoma (MB) samples with heterozygous SMARCA4 mutations do not group separately, but with established MB subgroups. RNA sequencing of ATRT-SMARCA4 confirmed the clustering results based on DNA methylation profiling and displayed an absence of typical signature genes upregulated in SMARCB1 deleted ATRT. In summary, our results suggest that, in line with previous clinical observations, ATRT-SMARCA4 should be regarded as a distinct molecular subgroup.

A rare manifestation of choriocarcinoma syndrome in a child with primary intracranial germ cell tumor and extracranial metastases: A case report and review of the literature.

Choriocarcinoma syndrome is an uncommon, potentially fatal complication of germ cell tumors (GCTs) in adults, but it is not well documented in children. Pediatric central nervous system (CNS) GCTs comprise a rare group of malignancies not usually associated with extra-CNS metastatic disease. Here, we report the case of a pediatric patient with a suprasellar mixed GCT and pulmonary metastases who presented with intratumoral hemorrhage and stroke. Choriocarcinoma syndrome developed soon after initiating chemotherapy. The primary tumor and pulmonary metastases were successfully treated using a multidisciplinary approach, including neurovascular intervention, chemotherapy, and craniospinal irradiation.

Treatment-related calvarial lesions in pediatric brain tumor survivors.

BACKGROUND: Despite improved survival, many pediatric brain tumor survivors receiving radiation therapy (RT) experience late effects. PROCEDURE: To study calvarial lesions in this population, we retrospectively reviewed records of patients undergoing neurosurgical evaluation for calvarial bone lesions detected in posttreatment follow-up imaging at St. Jude Children's Research Hospital. Primary tumor diagnosis, treatment, imaging, surgical intervention, and histopathology from patients with radiographic evidence of lesions followed for ≥2 years post-RT were studied. RESULTS: For 17 patients with 18 index lesions, median time to lesion manifestation was 2.34 years. Medulloblastoma patients developed lesions at a shorter interval from RT than ependymoma patients (P = .05). Twelve of 14 lesions requiring surgery were benign fibro-osseous or sclerotic. Two malignant lesions distinct from the primary tumor had genetic predisposition to malignancy. CONCLUSION: Most calvarial lesions arising post-RT are benign and fibro-osseous. Serial imaging is recommended, and high index of suspicion for malignant lesions is warranted for patients genetically predisposed to cancer.

Anaplastic Astrocytoma in a Child With Coffin-Siris Syndrome and a Germline SMARCE1 Mutation: A Case Report.

Coffin-Siris syndrome (CSS) is a rare congenital disorder with variable clinical phenotype consisting of developmental delay and characteristic facial features. It is caused by mutations in the chromatin remodeling switch/sucrose nonfermenting complex. Although SWI/SNF genes are widely implicated in tumorigenesis, only 8 cases of neoplasm have been reported in patients with CSS. We report a case of anaplastic astrocytoma (WHO grade III) in an 18-month-old child with CSS due to a de novo germline missense SMARCE1 mutation. Additional molecular features of the tumor are described as well. The role of missense SMARCE1 mutations in tumor predisposition in children with CSS should be further investigated to better inform genetic counselling.

Clinical Implications of Real-time Integrative Sequencing in Management of Patients With Suspected Germline BAP1 Mutations.

Germline mutation of BRCA-associated protein-1 has been implicated in the development of tumor predisposition syndrome and high risk for malignant mesothelioma, lung adenocarcinoma, uveal melanoma, and cutaneous melanoma. Here, we present the case of a patient with recurrent metastatic melanoma who was found to have germline BAP1 and somatic BRAF mutation by clinical genomic sequencing. Detection of a germline mutation prompted screening for other cancers and surveillance in family members. Prospective integrative sequencing for pediatric cancer patients may identify pathogenic germline mutations and may improve outcomes and treatment-related morbidity by early diagnosis of malignancy.

Malignant progression of a peripheral nerve sheath tumor in the setting of rhabdoid tumor predisposition syndrome.

Malignant progression of a benign or low-grade tumor in individuals with germline alteration of SMARCB1 gene is not well characterized. In a family in which two carrier children had germline SMARCB1 mutations and atypical teratoid rhabdoid tumor, we report malignant progression of a nerve sheath tumor over a 7-year period in an affected adult family member. Prompt identification of the germline SMARCB1 alteration and the resultant rhabdoid tumor predisposition syndrome can help guide genetic counseling and surveillance in affected family members.

Mortality in children with low-grade glioma or glioneuronal tumors: A single-institution study.

BACKGROUND: While pediatric low-grade glioma/glioneuronal tumors (LGG/LGGNTs) are considered slow-growing, indolent tumors with excellent long-term prognosis, mortality due to the disease is not unknown. Few studies have addressed the cause of death in this population. METHODS: Retrospective review of clinicopathologic and radiologic data for children 21 years or younger with LGG/LGGNT who died at St. Jude Children's Research Hospital between April 1985 and June 2015. Our primary objective was to determine the causes and timing of mortality in affected children. RESULTS: For the 87 eligible patients, median age at diagnosis was 7.7 years (range, 0.21-21 years), median age at death was 14.26 years (range, 0.58-32 years), and median time to death from diagnosis was 4.02 years (range, 0.21-24 years). Midbrain/thalamus was the most common tumor location (n = 34), followed by suprasellar/hypothalamic (n = 18) and cerebrocortical (n = 13). Astrocytoma not otherwise specified (n = 24), pilocytic astrocytoma (n = 23), and fibrillary astrocytoma (n = 11) were the predominant histologic diagnoses. Causes of death included progressive primary disease (PD) (n = 43), progression of PD with histological features of a high-grade glioma at progression or at autopsy (PD-HGG) (n = 15), second cancer (n = 3), suicide (n = 4), and vehicular accident (n = 3). Among the 15 patients with PD-HGG, 12 received radiation therapy before histologic confirmation of progression. CONCLUSIONS: PD and PD-HGG contributed to 66% of the mortality in our patient cohort. Early psychological intervention should be included as part of the multidisciplinary management approach of children with LGG/LGGNT to reduce the risk of suicide in vulnerable subjects.

Ataxia Telangiectasia and Cancer Predisposition: Challenges in Management.

Immune dysregulation and predisposition to malignancies are critical comorbidities in children affected with ataxia telangiectasia. In addition, these children exhibit increased toxicity to conventional cancer therapy and dose reductions have been proposed to prevent life threatening adverse effects. These modifications to the treatment regimen may result in suboptimal outcomes for these patients. Our report of 3 children with ataxia telangiectasia and cancer highlight the immense challenges in the management of these children, underlining the need for the development of novel, biological agents with reduced acute and long-term side effects in the treatment of cancers in these children.

Marked functional recovery and imaging response of refractory optic pathway glioma to BRAFV600E inhibitor therapy: a report of two cases.

BACKGROUND: Despite appropriate therapeutic interventions, progressive optic pathway glioma (OPG) in children may result in loss of vision and other neurologic morbidities. Molecularly targeted therapy against the MAP kinase pathway holds promise in improving outcomes while resulting in lower treatment-related toxicities. We report two children with refractory OPG who had a substantial and early reversal of their neurologic deficits and an impressive imaging response of their tumor to BRAFV600E inhibition therapy. METHODS: Two children with OPG (BRAFV600E-mutated pilocytic astrocytoma) who did not respond to at least one frontline therapy were treated with the oral BRAFV600E inhibitor vemurafenib. RESULTS: Both children had substantial visual compromise before start of therapy, with one child additionally having motor deficits. Both had an early improvement in their vision, and the second child showed a demonstrable improvement in motor weakness. This was accompanied by a decrease in tumor size, which was sustained at 6 months from therapy. Neither child had significant toxicities except for mild skin sensitivity to vemurafenib. CONCLUSIONS: BRAFV600E inhibitor therapy can potentially reverse visual and neurologic decline associated with progressive OPG. The clinico-radiologic response appears to be prompt and marked. Ongoing clinical trials using BRAFV600E inhibitors can help confirm these early promising findings.

High-grade glioma in infants and young children is histologically, molecularly, and clinically diverse: Results from the SJYC07 trial and institutional experience.

BACKGROUND: High-grade gliomas (HGG) in young children pose a challenge due to favorable but unpredictable outcomes. While retrospective studies broadened our understanding of tumor biology, prospective data is lacking. METHODS: A cohort of children with histologically diagnosed HGG from the SJYC07 trial was augmented with nonprotocol patients with HGG treated at St. Jude Children's Research Hospital from November 2007 to December 2020. DNA methylome profiling and whole genome, whole exome, and RNA sequencing were performed. These data were integrated with histopathology to yield an integrated diagnosis. Clinical characteristics and preoperative imaging were analyzed. RESULTS: Fifty-six children (0.0-4.4 years) were identified. Integrated analysis split the cohort into four categories: infant-type hemispheric glioma (IHG), HGG, low-grade glioma (LGG), and other-central nervous system (CNS) tumors. IHG was the most prevalent (n = 22), occurred in the youngest patients (median age = 0.4 years), and commonly harbored receptor tyrosine kinase gene fusions (7 ALK, 2 ROS1, 3 NTRK1/2/3, 4 MET). The 5-year event-free (EFS) and overall survival (OS) for IHG was 53.13% (95%CI: 35.52-79.47) and 90.91% (95%CI: 79.66-100.00) vs. 0.0% and 16.67% (95%CI: 2.78-99.74%) for HGG (p = 0.0043, p = 0.00013). EFS and OS were not different between IHG and LGG (p = 0.95, p = 0.43). Imaging review showed IHGs are associated with circumscribed margins (p = 0.0047), hemispheric location (p = 0.0010), and intratumoral hemorrhage (p = 0.0149). CONCLUSIONS: HGG in young children is heterogeneous and best defined by integrating histopathological and molecular features. Patients with IHG have relatively good outcomes, yet they endure significant deficits, making them good candidates for therapy de-escalation and trials of molecular targeted therapy.

Phase II Trial of Dabrafenib Plus Trametinib in Relapsed/Refractory BRAF V600-Mutant Pediatric High-Grade Glioma.

PURPOSE: BRAF V600 mutation is detected in 5%-10% of pediatric high-grade gliomas (pHGGs), and effective treatments are limited. In previous trials, dabrafenib as monotherapy or in combination with trametinib demonstrated activity in children and adults with relapsed/refractory BRAF V600-mutant HGG. METHODS: This phase II study evaluated dabrafenib plus trametinib in patients with relapsed/refractory BRAF V600-mutant pHGG. The primary objective was overall response rate (ORR) by independent review by Response Assessment in Neuro-Oncology criteria. Secondary objectives included ORR by investigator determination, duration of response (DOR), progression-free survival, overall survival (OS), and safety. RESULTS: A total of 41 pediatric patients with previously treated BRAF V600-mutant HGG were enrolled. At primary analysis, median follow-up was 25.1 months, and 51% of patients remained on treatment. Sixteen of 20 discontinuations were due to progressive disease in this relapsed/refractory pHGG population. Independently assessed ORR was 56% (95% CI, 40 to 72). Median DOR was 22.2 months (95% CI, 7.6 months to not reached [NR]). Fourteen deaths were reported. Median OS was 32.8 months (95% CI, 19.2 months to NR). The most common all-cause adverse events (AEs) were pyrexia (51%), headache (34%), and dry skin (32%). Two patients (5%) had AEs (both rash) leading to discontinuation. CONCLUSION: In relapsed/refractory BRAF V600-mutant pHGG, dabrafenib plus trametinib improved ORR versus previous trials of chemotherapy in molecularly unselected patients with pHGG and was associated with durable responses and encouraging survival. These findings suggest that dabrafenib plus trametinib is a promising targeted therapy option for children and adolescents with relapsed/refractory BRAF V600-mutant HGG.